1. Field of the Invention
The subject invention relates to a circuit for detecting and synchronizing a ghost cancellation reference signal contained in a television signal.
2. Description of the Related Art
U.S. Pat. Nos. 5,047,859 and 5,121,211 both to Koo disclose a signal which, when transmitted with a standard television signal, enables a corresponding circuit to correct said signal thereby eliminating "ghost", i.e., errors in the signal arising from, for example, reflections from buildings, terrain, etc. For a ghost canceler to be effective, the ghost cancellation reference (GCR) signal must be detected and stored digitally to be processed. The methods for the detection of this signal involve a determination of a particular line of the video signal from analog or digital video synchronization signal processors and then comparing this detected signal to a stored reference GCR signal. These processors are designed to accommodate standard NTSC signals or standard video signals with low S/N characteristics, but not ghosted signals. Ghosting causes the video synchronization levels to change dynamically line-to-line. Simple level-slicing methods are insufficient under ghosted signal conditions. This means that the horizontal synchronization pulses cannot be reliably counted with respect to the vertical interval, thereby introducing errors in determining the location of the GCR signal to be detected. Other methods involving sync. prediction use either differentiation or integration, or a combination of both, as feedback to the prediction algorithm. This means that the sync. processor can be stabilized, but the statistical error over a few lines can allow the predictor to be off by one or more lines resulting in an erroneous detection of the GCR signal.